The cleaning of integrated circuit (IC) substrates, such as silicon wafers, with metal-free alkaline solutions to remove organic and metal contamination is widely practiced. One commonly used alkaline solution of this type is known as SC-1 or RCA-1 and comprises an aqueous mixture of ammonium hydroxide, hydrogen peroxide, and water (1:1:5 of 30% H.sub.2 O.sub.2, 28% NH.sub.4 OH and H.sub.2 O). Various cleaning tasks can be accomplished with SC-1, among these, the cleaning of silicon wafers immediately after their fabrication, the cleaning of such wafers immediately prior to gate oxide growth, the removal of oxide etch residues later in the IC processing sequence, and selective etching and resist particulate removal. The purpose of the hydrogen peroxide is to protect the silicon metal from exposure to strong acids or bases by continuously forming a protective oxide layer in order to prevent etching or roughening of the silicon surface.
However, the presence of hydrogen peroxide in SC-1 formulations imparts an inherent instability to these solutions. Such solutions typically exhibit peroxide half-lives of less than one hour at 70.degree. C. The hydrogen peroxide in the SC-1 solution in the presence of certain metals, particularly copper and iron, becomes unstable and decomposes in rapid exothermic fashion leading to potentially dangerous conditions. The hydrogen peroxide has a low tolerance for metal contamination. Additionally, the decomposed hydrogen peroxide drops the concentration of the hydrogen peroxide leading to the possibility of silicon etching producing wafers that are not acceptable for IC manufacture. Thus, the decomposed hydrogen peroxide needs to be replenished and this changes the solution composition thereby varying the cleaning properties of the solution. In addition, the inherently high pH of the hydrogen peroxide solution presents undesirable safety and environmental concerns.
Hydrogen peroxide-free IC substrate cleaning solutions comprising simple aqueous solutions of quaternary ammonium hydroxides have been reported in Japanese Patent Publication No. 63-114132 and in U.S. Pat. No. 5,259,888. Oxide etch residue removal with such solutions has also been disclosed in EP Patent Publication 540,261 and Japanese Patent Publication No. 05-259066. However, as disclosed in U.S. Pat. Nos. 4,113,551, and 4,339,340, such solutions etch (poly)silicon and single crystal silicon wafers resulting in rough surfaces that may be unsuitable for further processing. During the later stages of IC wafer fabrication, the original polished silicon surface has been covered with various oxide and metal layers. However, the backside of the wafer remains exposed to process fluids and must be protected similarly to the initial polished silicon surface. This silicon etching and resulting surface damage may be prevented by including hydrogen peroxide in the alkaline cleaning formulation as disclosed in Japanese Patent Publication No. 3-93229 and U.S. Pat. Nos. 4,239,661, and 4,339,340. Other agents that reportedly suppress silicon etching include hydrazine as disclosed in Japanese Patent Publication No. 64-14924 and a certain nonionic surfactant, polyoxyethylene nonylphenol, as disclosed in U.S. Pat. Nos. 4,239,661, and 4,339,340. However, polyoxyethylene nonylphenol has recently been implicated as an environmental estrogen mimic.
It is therefore desirable that an alkaline cleaner solution be available which does not require the presence of hydrogen peroxide, that is, a cleaner composition in which the addition of hydrogen peroxide or other oxidizing agents is optional. More particularly, it is an object of this invention to provide such an alkaline cleaner solution that does not require the presence of hydrogen peroxide or other oxidizing agent yet produces an effective wafer cleaning action without producing undue wafer roughness sufficient to render the wafers unacceptable for IC manufacturing and processing, particularly for high density IC manufacturing. A still further object of this invention is to provide such an effective cleaning solution that can be used to clean vias in processed wafers of resist and etching residue, i.e. residual ash and organic and inorganic contaminants. A still further object of this invention is to provide such alkaline cleaning compositions for cleaning wafers and producing a roughness of less than about 25 Angstroms as the average distance in the Z direction between wafer peak heights and valleys.